This invention relates to a magnetic recording medium having a thin alloy film which has an axis of easy magnetization in a direction substantially vertical to the surface of the film and which is capable of recording information in high density by forming in the film a small reverse magnetic domain having a magnetic polarity opposite to the magnetic polarity of the film surface.
Three types of thin ferromagnetic films are known to have an axis of easy magnetization in a direction substantially vertical to the surface of the film and to have the ability to record information in high density by forming a small reverse magnetic domain upon exposure to light by virture of their Curie point or magnetic compensating temperature. The three types of thin ferromagnetic films include: (1) a thin film of polycrystalline metal typified by MnBi; (2) a thin film of an amorphous metal such as Gd-Co or Gd-Fe; and (3) a thin film of a single-crystal compound typified by GIG. However, these films are very difficult to produce, have a very small coercive force at room temperature or are very expensive.
A thin film of amorphous Tb-Fe or Dy-Fe has a high coercive force at room temperature, but according to Japanese Patent Application (OPI) No. 31703/77 (the term "OPI" as used herein means an unexamined published Japanese patent application), a thin amorphous film of Tb-Fe exhibits such property only when it contains 15 to 30 atomic% Tb, and, according to Japanese Patent Application (OPI) No. 109193/77, a thin amorphous film of Dy-Fe exhibits such desired property only when it contains 18 to 28 atomic% Dy.